Microbiological changes occurring in a soil under pasture and bare conditions
1931
Reuszer, H.W.
A soil under permanent pasture conditions and the same soil kept free of vegetation were studied from the point of view of microbiological factors of seasonal nitrate nitrogen accumulation under field conditions, accumulation of nitrate from the soil organic matter and from ammonium sulfate, rate of carbon dioxide evolution, and numbers of micro-organisms. The results can be summarized as follows: The soil growing pasture grasses had an extremely low and almost constant nitrate content. The same soil without growing plants accumulated considerable quantities of nitrate, the amount of which exhibited a seasonal fluctuation which seemed to be correlated with the accumulated rainfall. There is evidence also that part of the autumn rise in soil nitrate may be due to mineralization of nitrogenous microbial complexes. The nitrate accumulation from the soil organic matter was 35% greater in soil from pasture plats than in soil from bare plats. A slightly greater nitrification of ammonium sulfate was found in the bare soil than in the pasture soil. The low nitrate values in the grass soil were not due to a lack of nitrifiable organic matter or of a nitrifying flora. The production of carbon dioxide from the pasture soil was on the average 194% of that from the bare soil. This indicates a much greater microbiological activity in the pasture soil. Significant differences in total numbers of micro-organisms as determined by the plate method were not found. Fungi and actinomyces were more numerous in the pasture than in the bare soil. The B. radiobacter group was twice as numerous in the pasture as in the bare soil.
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